Traditionally web/ria frameworks/toolkits have been fairly monotilic: even though many of the frameworks are designed to be extensible, it has been painful to build, package and distribute a new user interface component. This have lead to situation where framework vendors mostly bundle all the functionality inside the framework - in order to make it easy to be use.

As as result - those brave developers who have built and released add-ons to frameworks have been "second class citizens" from the point of view of framework users - it is simply just so much easier to use built-in functionality than test and integrate third party add-ons. Partly because of this - many of the add-on ecosystems have not been too lively and users mainly had to live with whatever functionality the framework vendor has built into the framework.